1. Technical Field
This invention relates generally to processing substrates and more specifically, to an automated system for handling thin substrates requiring thin-film coatings, such as magnetic and optical disks, wafers, lenses, and glass panels and the processing of the substrates within a series of process chambers.
2. Discussion of Prior Art
Sputtered thin films are widely employed in the manufacture of magnetic and optical disks, wafers, lenses and glass panels. Magnetic and optical disks are used in mass storage devices for digital information. The competitive nature of the digital storage market continues to force media manufacturers to produce disks with greater storage capacities and at lower costs. The equipment used to produce the disks must meet these demands by providing increased throughput, higher quality product, improved yield, greater uptime, reduced maintenance, more flexibility, and lower purchase and operating costs.
There are a number of prior art systems which handle and process substrates for magnetic and optical media. Such deposition systems fall into two general categories: in-line sputtering systems and static sputtering systems.
In-line systems typically carry a large number of substrates arranged on a pallet. The pallet is loaded in the atmosphere then introduced into the system. Typically, the pallet moves continuously through the system during the processing of the substrates. Processing often occurs in a common vacuum chamber while the pallets are in motion. While this methodology has a distinct throughput advantage it has a number of disadvantages. Because processing occurs while the substrates are in motion relative to the process stations, the quality and uniformity of the applied coatings are sacrificed. Since processing often occurs in a common chamber, a process in one station can contaminate a process in another. The pallets are commonly partially coated incidentally along with the substrates. Because the pallets are repeatedly coated, the coating begins to flake, creating particulates that are detrimental to the substrates and equipment. Exposure of the pallet to atmosphere after each production run exacerbates the flaking problem. Therefore, the pallet and transport systems require frequent, extensive and costly servicing and cleaning.
Static sputtering systems typically load one substrate into a process station at a time and sequentially process each substrate in isolation from other substrates being processed, with no relative motion between substrate and the deposition source during the processing. The components that handle the substrates during processing are not exposed to the atmosphere. Instead, the substrates are loaded into the vacuum chamber through a load lock chamber and then transferred onto the substrate handling components. The disadvantages of inline systems are thus largely reduced or eliminated. Although inline systems have superior throughput, static systems are more capable of producing the high quality media demanded by the market.
U.S. Pat. No. 5,215,240 to Berg et al. discloses a static sputtering system that supports substrates in a vertical orientation and moves the substrates through the system in a sequential, circular pattern. The substrates are transported into the system by a conveyor system using sets of gear-driven rollers. Individual substrates are removed from a cassette by a lift blade, then transferred from the lift blade to the main chamber transport. Once deposited onto a pedestal on the main chamber transport the substrate is moved sequentially through a series of process chambers congruous with the main chamber. The main chamber transport moves downward, rotates the pedestal to be under a process station, then moves upward until the substrate is in a process chamber where the first of a series of processes can occur. Each substrate is processed in isolation from the other substrates. This down, rotate, up, process sequence continues until the substrate has been fully processed and removed from the main chamber transport and while other substrates are continually loaded, processed, and unloaded. After being removed from the main chamber transport the substrate is placed in a cassette which, when full, is removed from the system through an unload lock chamber.
The large number of moving parts within the vacuum chamber are detrimental to the quality of the vacuum and tend to generate particulate matter, require careful alignment, need continuous maintenance, and are not easily accessible. The high vacuum pumps are located several feet from the process chambers they pump, limiting conductance. Dimensional changes to the system, due to thermal expansion and pressure differentials, reduce transport reliability and necessitate the use of complicated compensation methods. The three-motion index of the main chamber transport system limits the throughput of the system and reduces transport reliability. Additional limitations, some shared by other commercially available static sputtering systems, include:
(a) large chambers that are inflexible and expensive to manufacture, and therefore are not readily adaptable to customer needs; PA1 (b) high-vacuum pumps that are used on one side of the process chamber and result in asymmetrical pumping, pressure differentials within the chamber, and non-uniform process parameters; PA1 (c) complex cassette handling systems that are difficult to align, suffer reliability problems, and generate particulate matter; PA1 (d) complex substrate handling systems that require precise alignment and extensive maintenance, and are prone to substrate mishandling and excessive downtime; PA1 (e) handling systems that contact the substrate several times and correspondingly increase the probability of damaging the substrates; PA1 (f) complex handling systems that are costly, reduce vacuum quality and make troubleshooting difficult; and PA1 (g) handling systems that require several modifications in order to accept differently-sized cassettes and substrates. PA1 (a) a potential throughput superior to prior art static sputtering systems, PA1 (b) a system capable of achieving superior vacuum, PA1 (c) symmetrical high vacuum pumping within close proximity of the process stations, avoiding convoluted, conductance limiting pathways, PA1 (d) a simple handling system that minimizes the number of moving parts, particulate generation, calibration, maintenance and downtime, and is less sensitive to dimensional changes to the system during operation, PA1 (e) a system capable of handling a variety of cassette sizes without requiring adaptation of the handling system, PA1 (f) a system capable of handling a variety of substrate sizes with minimal adaptation of the system, PA1 (g) a handling system that reliably suspends each substrate, PA1 (h) a transport system which handles the substrates as little as possible, and PA1 (i) a system that is less costly to manufacture.